[F:1][C:2]1[C:7]2[NH:8][C:9](=[O:11])[O:10][C:6]=2[C:5]([C:12]([OH:14])=O)=[CH:4][CH:3]=1.C(Cl)(=O)C([Cl:18])=O>ClCCl.CN(C)C=O>[F:1][C:2]1[C:7]2[NH:8][C:9](=[O:11])[O:10][C:6]=2[C:5]([C:12]([Cl:18])=[O:14])=[CH:4][CH:3]=1A stirred suspension of 4-fluoro-1,3-benzoxazol-2-one-7-carboxylic acid (1.79 g) in dry dichloromethane was treated with oxalyl chloride (0.97 g), followed by N,N-dimethylformamide (3 drops) to initiate the reaction. Stirring was maintained under reflux conditions for 1.5 hours and the mixture evaporated to dryness to give 4-fluoro-1,3-benzoxazol-2-one-7-carboxylic acid chloride, used in the next stage without purification.
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